Population synchrony as a measure of habitat specificity and movement patterns in a nomadic finch, the red crossbill (Loxia curvirostra)

Measures of the spatial scale of population synchrony provide valuable information on the role of dispersal and environmental variables in population dynamics.  In addition, spatial patterns of population synchrony may also reveal patterns of resource tracking and large-scale habitat specificity among sub-populations that influence movement patterns and subpopulation structure.  Numerous bird species of coniferous forests in North America rely on the masting production of conifer seeds that fluctuate over large spatial areas.  Red crossbills rely on continent-scale movements to locate new areas each year with abundant conifer seeds and are unique in that they are characterized by several different morphological forms.  Foraging trials in captivity have suggested that these different types may specialize on specific conifer species and this may influence the scale and frequency of movements.  However, the degree to which red crossbills are food specialists in the wild and how this might influence population dynamics is unknown.  Using North American Breeding Bird Survey and Christmas Bird Count data from over 30 years, I measured habitat-specific continent-scale patterns of population synchrony in red crossbill abundance to examine their large-scale movements and determine whether population synchrony among regions is influenced by habitat type.  Population synchrony is greater among sites and regions that are dominated by the same conifer used by red crossbills.  In addition, the spatial extent and pattern of synchrony among habitat types varies, possibly reflecting species differences in spatio-temporal cone production among conifers that influence population movements of crossbills.